This invention relates to optical fibers and, in particular, to a method and apparatus for extracting optical energy or light from such fibers.
Optical fiber taps are known in the art in which optical energy or light is extracted from an optical fiber by bending the fiber. U.S. Pat. No. 4,802,723 discloses a fiber tap of this type in which the tap comprises a transparent tube which surrounds the fiber and has a detector at an end of the tube following the bent portion of the fiber. The detector receives light escaping from the fiber at the bent portion. The transparent tube is shown as either a straight tube which surrounds the fiber portion following the bent section or a bent tube which surrounds the bent section of the fiber and the fiber portions fore and aft of the bent section.
In fiber taps and couplers of the above type, the radius of curvature at the bend and the angle of the bent section determine the fraction of the optical energy extracted from the fiber. If it is desired that the extracted energy be relatively large (as might be required for taps and couplers situated further down a fiber optic transmission line), the radius of curvature at the bend must be relatively small.
As the radius of curvature at the bend of the fiber becomes smaller, however, the fiber becomes more susceptible to breaking, since the tension at the radially outer portion of the bent section of the fiber may exceed the fracture point of the fiber. For example, a bend of 0.5 cm radius causes a tensile strain of 1.25% at the outside of the bend for a typical optical fiber of 125 microns diameter. A strain of this amount can cause a bulk sample to fracture and, in addition, the stress is greater than the proof stress of usual optical fibers of this type.
It is therefore a primary object of the present invention to provide an apparatus and method for extracting optical energy from or coupling optical energy into a fiber which avoids the above disadvantages.
It is a further object of the present invention to provide an apparatus and method for extracting optical energy from or coupling optical energy into a fiber in which the likelihood of breaking of the fiber is reduced.
It is yet a further object of the present invention to provide an optical fiber tap or coupler for use in extracting optical energy from or coupling optical energy into the bent portion of an optical fiber in such a manner that the likelihood of fracture of the fiber at the bent portion is reduced.